Steel tubes or pipes lined with plastic linings is a new water supplying material in buildings, which is a substitute for tubes which are made of only plastic thanks to the corrosion-resistant inner side and high strength due to the outside steel, and is more and more popular in the market. Some of conventional steel tubes or pipes are combined with their plastic linings by using electricity, oil, gas or natural gas to heat steel tubes or pipes and heat the plastic linings through transferring of the heat from the steel tubes or pipes to the plastic linings, wherein the heat is produced by using electricity, oil, gas or natural gas and carried by wind to heat the tubes or pipes directly with the hot wind, which results in un-uniform heating and loose adhesion of the steel tube or pipe with its lining or bad adhesion in some parts, which in turn tends to cause divorce of the lining from the steel tube or pipe after expansion and contraction due to temperature difference and cause un-alignment of the ends of the steel tube or pipe with the ends of the plastic lining, and cause contraction of the plastic lining so that the quality of the steel tube or pipe lined with plastic lining is not the optimum While others are produced by binding the plastic linings to the inner sides of the steel tubes or pipes with adhesive or binder, e.g. WO2004/011231.
Any process in the prior art for manufacture of steel and plastic combined tubes or pipe is among the labor intensive industries, which is not equipped with matching NC equipments or conveying arrangements and is not in good condition in view of mechatronics, and therefore needs hard working with the disadvantage of low control precision and high rate of defective products. Furthermore, products with steel tubes or pipes of different spec or thick of wall, or with linings of different plastic can not be produced at different environmental temperature and/or different environmental humidity.